IGN DS has their hands on the first US-release DS Option Pak, the DS Rumble Pak, and has posted an article examining it.
The article notes that only Metroid Prime Pinball currently supports the Rumble Pak. Future titles will have to be made Rumble Pak-aware in order to use the accessory. In addition, IGN has noted that their Rumble Pak is very noisy to the point of annoyance, speculating that theirs may indeed be defective.
The DS Rumble Pak will be included with the upcoming Metroid Prime Pinball, scheduled to release October 24.